The present invention relates to a multi-channel recording instrument.
In a multi-channel recording instrument, various signals are simultaneously recorded on a same recording paper. There is provided one each channel equipment for each signal of the various signals. For example, when eight signals are to be recorded simultaneously, eight channel equipments are provided. Each channel equipment has a reference signal input means, an error detector means for generating the error signal from the difference between the reference signal and the corresponding feedback signal, a servo-amplifier for amplifying the error signal, a servo-motor driven by the output of the servo-amplifier, and a recording pen which is positioned by the servo-motor. Since the feedback signal is determined by the position of the pen, the position of the pen of a channel is feedback-controlled by the reference signal of the channel.
Generally, all the recording pens of a multi-channel recording instrument move on a same line. When this line is denoted by the X-axis of rectangular coordinates, the paper-feed of the recording paper is in the direction of the Y-axis which is perpendicular to the X-axis.
And, in a multi-channel recording instrument, the biasing voltage of the reference signal may be different for each channel. And, therefore, all the circuits which are conductively connected to the reference signal input terminal must be connected to a floating power-supply.
In a heretofore known multi-channel recording instrument, all the circuits of each channel equipment, which includes a reference signal input means, an error detector means, a servo-amplifier, and a servo-motor, are connected to a floating power supply of the channel. Since the servo-amplifier and the servo-motor consume a considerable power, the floating power-supply of a channel must have a fairly large capacity. When there are eight channels in a multi-channel recording instrument, eight such floating power-supplies of fairly large capacity must be provided. This makes the whole power-supply system bulky and expensive. This is one of the disadvantages of the heretofore known multi-channel recording instrument.
Another disadvantage is in the mounting of the servo-motors. The potential level of the reference signal in relation to the earth potential may be high, raising the potential level of the floating power-supply to the same height in relation to the earth potential. Therefore, the casing of the servo-motor must not be grounded, because the insulation between the winding and the casing of the motor is not sufficient against the high voltage between the floating power-supply which is connected to the winding and the earth potential. Since the chassis of the instrument must be grounded, the servo-motor must be mounted to the chassis through insulating material which can withstand the voltage between the floating power-supply and the ground. This will increase the assembly cost and the size of the instrument.